There is known U.S. Pat. No. 4,149,585 relating to a method for transferring heat between fluids with geothermal application. This invention uses the principle of a cascading heat transfer using the same refrigerant from compressor to compressor thus increasing its temperature. This is an efficient but very costly system.
There is also known U.S. Pat. No. 4,413,669 for a method of heat extraction from water through a expansion in stages.
There is also known U.S. Pat. No. 5,025,634 for a heating and cooling device that uses the earth's thermal energy. This device generates heat or cold through a heat pump that reverses the refrigerant flow depending on whether heat or cold is desired. There is a loss of efficiency in this design considering that the heat pump cannot perform both heating and cooling duties at maximum efficiency due to the fact that latent heat and thermal capacity of a liquid (for cooling) and vapor (for heating) are different.
There is also known U.S. Pat. No. 5,564,282 relating to a system for extracting thermal heat; this invention uses a heat pump as described in U.S. Pat. No. 5,025,634 and multiple parallel ground loops that can be cut off from the system individually to evacuate refrigerant in the cooling mode.
There is also known U.S. Pat. No. 4,391,104 from Jul. 5, 1982. The invention works in three modes, as described below:
First mode performs water heating with coil 14 and ambient air cooling with coil 23; this mode uses the first loop only. The heating condenser temperature should be 60° C. to be functional. The cooling evaporator temperature should be at least 15° C. to perform a reasonable cooling effect.
Third mode performs air heating with coil 31 and cooling fresh outside air with coil 38. This mode uses the second loop only. The heating condenser temperature should be at least 30° C. to get a feeling of a heating effect. The cooling evaporator temperature should be at less at −10° C. to be able to exchange in the winter condition.
Second mode is the water heating by cooling fresh air from outside, this mode uses two loops to perform water heating and cooling fresh air. The first loop should stays in accordance with the first mode. The second loop should stays in accordance with the third mode.
Minimum temperatures are as follows:                cooling ambient air (15° C.)        cooling fresh air in winter condition (−10° C.)        heating ambient air (30° C.)        heating water (60° C.)        
The second mode is the closest prior art to the present invention, but major different between both systems is described below:
A minimum overlap temperature of 15° C. has to exist between first loop evaporator coil 23 and condenser coil 31. This overlap is very high compared to 4° C. for the present invention. This high overlap temperature result in efficiency losses from compressors and significantly affects the total efficiency of the bolt loop staged. This invention has a fixed overlap temperature compared to the present invention that can use many different combinations without affected heating ambient air temperature and cooling ambient temperature. This invention has a limited heating ambient air temperature compared to the present invention set at heating ambient air at 60° C. The tri-fluid exchanger 22 is used to stage energy to second loop and as cooling and heating coil. In the present invention, the coaxial staging exchanger 4 is used only as a bi-fluid heat exchanger. When in second mode, efficiency loses will occur on the tri-fluid coil 22 in an air duct because the aluminum fin core from the tri-fluid coil 22 will exchange with air from air duct instead of transferring to another loop. In the present invention, the coaxial staging exchanger 4 is insulated; when there is insulation around outer tube, there are no energy losses in the exchange with ambient air.